Many electronic systems control on-chip voltages from external power supply sources using linear dropout regulators (LDOs) formed of transistors and capacitors rather than inductors. Such low-dropout regulators serve as direct current (DC) linear voltage regulators that can regulate the output voltage even when the supply voltage is very close to the output voltage.
LDOs have become available for use in on-chip circuitry. Bringing LDOs on-chip has the desirable effect of reducing parts counts, reducing chip I/O (input/output or IO) count, and improving reliability of the electronic system 100. However, on-chip LDOs introduce several undesirable characteristics. Specifically, because these on-chip LDOs use transistors and small capacitors rather than relatively large inductive components and relatively large capacitive components, during operation, these on-chip LDOs introduce undesired voltage transients or ripples at their outputs. When the load on the LDO is small, the voltage swings during rippling can oscillate through overshoots and undershoots—sometimes undershooting to a voltage level well below brownout voltages. As a result, circuitry powered by the LDO may exhibit unwanted behavior (e.g., spontaneously resetting) when the rippling voltage drops below the brownout voltages of the downstream circuit components.
In certain electronic systems, portions of the electronic system 100 including the LDOs can be powered down or placed in a low-power mode during periods when portions of the electronic system 100 are inactive, such as when in a sleep, or dormant, or hibernating mode. Switching between such modes may cause the LDOs to exhibit the unwanted transients described above. Such transients may cause downstream circuitry to receive voltages below their brownout voltages, which in turn can cause such circuitry to fail. Thus, it may be desirable to eliminate or mitigate voltage transients that occur at the outputs of the LDO regulators when changing power modes.